1. Field of the Invention
The present invention relates to a flat-plate-shaped electroluminescence lamp (hereinafter referred to as an EL lamp) using an electroluminescence element (hereinafter referred to as an EL element) for a light source, specifically to an EL lamp having a mechanical tolerance of the bending load applied in attaching the element to and detaching it from a power supply outlet in a repeated manner, and a method of use thereof.
2. Description of the Prior Art
EL refers to a luminescence produced when a voltage is applied to a luminous layer wherein a phosphor such as zinc sulfide is doped with the materials of luminescence such as manganese and copper. In the luminous layer whereto a voltage is applied, the materials of luminescence (atoms serve to cause luminescence) are excited to the unstable state of high energy from the stable state of low energy, and when returning again to the stable state of low energy, they emit excess energy as light. The EL element has various features such that the thickness of the luminous layer can be made very small, for example, as thin as several dozens of microns or less, uniform light is obtainable from the whole luminous surface, various colors of luminescence are obtainable, and a heat generating action does not occur. At present, although having problems of brightness and life, such lamps have been considered to be usable for wall illumination with the whole wall acting as a light source and for small-size, light-weight displaying apparatuses in place of cathode ray tubes, and has been put in practical use partly for back lighting of meters for automobile, ships, aeroplanes, and the like, back lighting of liquid crystal displays, display portions of portable measuring equipment, panel displays for personal computers and the like.
As described above, the EL element differs basically from other luminous bodies in that the luminous layer thereof can have a thickness of about several dozens of .mu.m, and the conventional EL lamps have made use of this feature to a maximum extent, and have been used widely for thin stationary types of lights wherein substantially no mechanical strength is required. For example, in U.S. Pat. No. 4,626,742, an EL lamp is disclosed wherein an EL element is formed on a thin film composed of polyethylene terephthalate 127-178 .mu.m (0.005-0.007 inch) in thickness. This EL lamp can hardly be said to have a satisfactory mechanical strength, and therefore has a problem of easy deformation by an external force, but because of this thinness, it is suitable for stationary use in a narrow place, for example, in a small-sized electronic component.
On the other hand, the present inventors have achieved the present invention on the basis of a finding that, quite the reverse to the conventional direction of development of the EL lamps, a flat-plate-shaped EL lamp having a large mechanical overall strength can respond to various requests for such lamps made in recent years as described later, even if the thickness thereof becomes a little larger.